1. Technical Field
The present disclosure relates to a phosphor and a light-emitting device including the phosphor. The present disclosure also relates to an image pickup device, a liquid crystal display device, and a lighting device, each including the light-emitting device. The present disclosure further relates to a vehicle including the lighting device serving as a vehicle lighting device.
2. Description of Related Art
From the viewpoint of energy saving, white LEDs (light-emitting diodes) have been widely used in recent years.
At present, commonly available white LEDs have a configuration in which a blue light-emitting element (blue LED chip) and a phosphor are combined. In such a commonly available white LED, a portion of blue light emitted from a blue LED chip is color-converted with a phosphor so that the blue light emitted from the blue LED chip and the light emitted from the phosphor are mixed to produce white light.
At present, combinations of blue LED chips and yellow phosphors are dominant in white LEDs. However, combinations of LEDs that emit light in the blue to near-ultraviolet region and three types of phosphors, i.e., blue phosphors, green phosphors, and red phosphors have been studied to develop white LEDs with higher color rendering properties and higher color reproducibility.
More recently, combinations of laser diodes (LDs) and blue, green and red phosphors have also been studied to develop high-power white light emitting devices.
Blue phosphors represented by the general formula: M3MgSi2O8:Eu2+ (where M is at least one element selected from Ca, Sr, and Ba) are conventionally known. However, these blue phosphors have the drawback of low emission quantum efficiency. In order to overcome this drawback, JP 2009-280793 A discloses, as a phosphor with improved quantum efficiency, a phosphor containing an Eu-containing M13MgSi2O8 based crystal (where M1 is Sr and Ba) as a main crystal and a M12MgSi2O7 based crystal which is known as a crystal capable of emitting cyan light. However, the quantum efficiency of the phosphor disclosed in JP 2009-280793 A is still lower than required.